Use of heterogeneous acid catalysts based on mixed metal salts to produce biodiesel

Abstract

The present invention relates to the production of biodiesel and alkyl esters by the transesterification of triglyceride esters, with alcohols in heterogeneous phase in the presence of heterogeneous catalysts, with yields higher than 80%, at a temperature from 0 to 300° C., residence time from 20 minutes to 20 h, space velocity of 0.1 to 10 h−1, pressure of 25-100 kg/cm2 (24.5-98.07 bar), methanol/oil molar ratio of 10 to 40 and catalyst concentration of 0.001 to 20 weight % based on tri-, di- or monoglyceride. The method produces biodiesel and alkyl esters by transesterification of tri-, di- or mono-glycerides, from palm, jatropha, castor, soybean and sunflower oils, wherein the alcohoxyls R1O, R2O and R3O of the glycerides are C1 to C24 and a C1-C4 alcohol, such as methanol, in an alcohol:oil ratio from 3:1 to 50:1. The transesterification reaction produces biodiesel while avoiding loss of catalyst, contaminating liquid effluents and eliminating undesirable hydrolysis of triglycerides, diglycerides and monoglycerides into free fatty acids and saponification that generate soaps.

What is claimed is: 
     
       1. A method of producing biodiesel by the transesterification of triglyceride esters with alcohols in the presence of a heterogeneous acid catalyst primarily Lewis acid in nature in heterogeneous phase, wherein said heterogeneous acid catalyst comprises mixed metal salts of lithium and aluminium phosphates and/or sulfates in a reactor, said method comprising feeding the triglyceride esters and alcohol to the reactor in batch or continuous flow, in descending or ascending mode, to obtain yields exceeding 80%, at the following operating conditions: temperature from 150 to 300° C., residence time from 20 minutes to 20 h, space velocity from 0.1 to 10 h −1 , pressure 25-100 kg/cm 2  (24.5-98.07 bar), alcohol/oil molar ratio of 10 to 40 and catalyst concentration of 0.001 to 20 weight % based on tri-, di- or monoglyceride. 
     
     
       2. The method of producing biodiesel according to  claim 1 , wherein the heterogeneous acid catalysts of mixed metal salts of lithium and aluminum phosphates and/or sulfates further comprise lithium in an amount of up to 5 weight %, and aluminum up to 15%, in addition to combinations with metal cations in concentrations of up to 40 weight % of the catalyst, where the metal cations are selected from the group consisting of magnesium, titanium, zinc, zirconium, gallium and silicon, to provide Lewis acidity; organic or inorganic porosity promoters in concentrations of from 0.05 to 25 weight % of a wet base catalyst, and binders in concentrations of 1 to 20 weight % of the catalyst, selected from the group consisting of clays, kaolin and metal oxides of the formula MxOy, where M=Al, Mg, Sr, Zr or Ti, X=1 or 2 and y=2 or 3, as particles selected from the group consisting of extrudates, spheres, trilobules and raschig rings. 
     
     
       3. The method of producing biodiesel according to  claim 2 , wherein the mixed metal salts of the catalyst, in addition to combinations with metal cations, are selected from the group consisting of:
 a. Phosphates and sulfates of lithium and aluminum, 
 b. Lithium, aluminum and titanium phosphates and sulfates, and 
 c. Phosphates and sulfates of lithium, aluminum and magnesium. 
 
     
     
       4. The method of producing biodiesel according to  claim 2 , wherein the porosity promoter is amylose-amylopectin (starch). 
     
     
       5. The method of producing biodiesel, according to  claim 2 , wherein the clays as binders are montmorillonite. 
     
     
       6. The method of producing biodiesel according to  claim 2 , wherein the catalyst has a surface area of 10 to 180 m 2 /g, pore volume from 0.1 to 0.5 cm 3 /g, and average pore diameter from 100 to 200 Å. 
     
     
       7. The method of producing biodiesel according to  claim 1 , wherein the transesterification of triglyceride esters with alcohols in a heterogeneous phase is carried out using vegetable oils selected from the group consisting of palm oil, jatropha, castor, soybean and sunflower, and a C 1 -C 4  alcohol in an alcohol: oil ratio of 3:1 to 50:1. 
     
     
       8. The method of producing biodiesel according to  claim 1 , wherein the transesterification of triglyceride esters with alcohols in heterogeneous phase in batch reaction systems is carried out in stirred tank with residence times from 20 minutes to 20 h. 
     
     
       9. The method of producing biodiesel according to  claim 1 , wherein the transesterification of triglyceride esters with alcohols in a heterogeneous phase in continuous flow reaction systems is carried out in a packed reactor flow rate in descending or ascending mode, at a space velocity of 0.1 to 10 h −1 , a pressure of 25 to 100 kg/cm 2 , a temperature of 150 to 300° C. and a methanol/oil molar ratio of 10 to 40. 
     
     
       10. The method of producing biodiesel, according to  claim 1 , wherein the transesterification of triglyceride esters with heterogeneous phase alcohols in continuous, ascending or descending flow is carried out in combination with other catalytic materials of a basic nature selected from the group consisting of magnesium oxides, aluminum oxides and sodium oxides to simultaneously promote the esterification and transesterification reactions. 
     
     
       11. The method of producing biodiesel according to  claim 7 , wherein the transesterification of triglyceride esters with alcohols in heterogeneous phase in batch reaction systems is performed in stirred tank with residence times of 20 minutes to 20 h. 
     
     
       12. The method of producing biodiesel according to  claim 1 , wherein the transesterification of triglyceride esters with heterogeneous phase alcohols is carried out in a continuous flow reactor in a descending or ascending manner at a space velocity of 0.1 to 10 h −1 , a pressure of 25 to 100 kg/cm 2 , a temperature of 150 to 300° C. and a molar ratio of methanol/Oil from 10 to 40. 
     
     
       13. The method of  claim 2 , wherein said catalyst includes 0.1 to 3 weight % lithium and 0.3 to 10 weight % aluminum. 
     
     
       14. The method of  claim 2 , wherein said metal cation is selected from the group consisting of titanium, magnesium and silicon and where said metal cation is present in an amount of 0.2 to 30 weight % based on the weight of the catalyst. 
     
     
       15. The method of  claim 2 , wherein said porosity promoter is a polysaccharide. 
     
     
       16. The method of  claim 2 , wherein said binder is a clay in the amount of 3 to 15% weight %. 
     
     
       17. The method of  claim 2 , wherein the catalyst has a surface area of 30 to 80 m 2 /g, a pore volume of 0.1 to 0.3 cm 3 /g, and an average pore diameter of 110 to 170 Å. 
     
     
       18. A method of producing biodiesel, comprising the steps of:
 feeding a triglyceride ester and an alcohol to a reactor in the presence of a heterogeneous acid catalyst primarily of Lewis acid in nature, wherein said heterogeneous acid catalyst comprises mixed metal salts of lithium aluminium phosphates, lithium aluminum sulfates, and mixtures thereof in the reactor; and 
 transesterifying the triglyceride in the presence of said catalyst at a temperature from 150 to 300° C., at a residence time from 20 minutes to 20 h, a space velocity from 0.1 to 10 h −1 , a pressure 25-100 kg/cm 2  (24.5-98.07 bar), alcohol/oil molar ratio of 10 to 40, and catalyst concentration of 0.001 to 20 weight % based on the triglyceride. 
 
     
     
       19. The method of  claim 18 , wherein said catalyst further comprises a cation selected from the group consisting of magnesium, titanium, zinc, zirconium, gallium, and silicon. 
     
     
       20. The method of  claim 19 , further comprising 0.05 wt % of an organic or inorganic porosity promoter, and 1-10 wt % of a binder selected from the group consisting of clays, kaolin and metal oxides of the formula MxOy, where M=Al, Mg, Sr, Zr or Ti, X=1 or 2 and y=2 or 3. 
     
     
       21. The method of  claim 19 , wherein said catalyst comprises said lithium in an amount of up to 5 wt %, and aluminum in an amount of up to 15 wt %, and said cation in an amount of up to 40 wt % based on the weight of the catalyst.